This invention relates to improved techniques for battery grid manufacture. Lead-acid batteries and their operation are well-known. The grids are the support for the active material of the plates and conduct the current to and from the active materials. The grid must be corrosion resistant and must possess sufficient strength and stiffness to prevent damage or distortion during manufacture of the grids, preparation of the plate from the grid and construction of the battery itself. Pure lead is the most corrosion resistant material for lead-acid battery grids, but it is weak and tends to creep. In use, the grids are subject to stress due to their own weight and the weight of active material supported by the grids and the stresses imposed through expansion and contraction of the active material in the charge-discharge cycle. If the grids are broken during use, the active material is isolated or shed and lost for the electrochemical reaction. From the standpoint of economies of weight, cost and cell capacity, grid thickness is also a significant factor.
Battery grids are generally made by a casting process. The grid-casting machine consists of a book or center-parting grid mold, trimming mechanism and melting pots. The grid mold consists of two cast iron parts, each with a grid design for a face. In order to avoid premature solidification the mold is heated before introduction of the molten metal. The lead or lead alloy is first melted in the melting pots and transported to the grid mold. After the mold is filled with molten metal, it is allowed to cool. It is then opened, the cast grid is removed and the operation begins anew for fabrication of the next grid. This is done on a mass production schedule and it is important that no undue delay occurs in the cycle.
Alloys are generally used as the preferred grid material because pure lead is easily deformed. The proper selection of the lead alloy depends on the intended use and economics of the lead-acid battery application because the alloys often introduce other problems such as cost, corrosion, difficulties in manufacture or reduced battery life.
Reinforcement of grids is a relatively new concept and shows promise of resolving many of the problems mentioned above. Efforts to use fiber to reinforce the grid structure have been found to present new problems in manufacture. Hand lay-up of filaments in the open casting mold is a time-consuming operation that is inconsistent with mass production techniques. Also, conditions around the grid casting area are not conductive to careful hand lay-up of the filaments. In some cases handling of the filaments causes discontinuities and breaks. When this occurs in the casting mold, it results in poor quality grids. The novel preform of the instant invention offers a solution to these problems.